The northern right whale dolphin (Lissodelphis borealis) is a small, slender species of cetacean found in the cold and temperate waters of the North Pacific Ocean. Lacking a dorsal fin, and appearing superficially porpoise-like, it is one of the two species of right whale dolphin.

Description

The northern right whale dolphin has a streamlined body with a sloping forehead, and a slimmer build than other delphinids. It lacks any fin or ridge on the smoothly curving back. Its body is nearly all-black with a white ventral marking, extending forward as a narrow band from the caudal peduncle to the throat region, where the patch widens. In females, this white band is wider in the genital area than in males. In southern right whale dolphins (Lissodelphis peronii), the white patch extends higher on the posterior flanks and head. Calves, which are born initially creamy-dark grey or brown, attain adult colouring by the age of one year.

The beak of northern right whale dolphins is short and well-defined, characterised by a straight mouthline. The flippers are small, curved, narrow and pointed. The tail flukes are triangular and, like the flippers, rather pointed.

Adults are long and weigh between . Females (2.3–2.6 m) are generally smaller than males (around 3 m). Otherwise the sexes appear similar.

Northern right whale dolphins have between 80 and 95 thin, sharp teeth, which are not externally visible, used for catching small fish and squid.

Data on growth and reproduction of right whale dolphins is limited. Examination of northern right whale dolphins caught in driftnets allowed for an estimation of the average age of sexual maturity; in males, it was estimated to be 9.9 and 10.1 years and, in females, 9.7 and 10.4 years. Average length at sexual maturity was estimated at 215.1 cm and 214.7 cm in males and 201.1 cm and 199.8 cm in females. The mass of a mature testis was between 117.4 g to 1300 g. Gestation period was 12.1 to 12.3 months and calving seemed to peak during summer (July and August). The minimum calving interval was two years. An asymptotic length of 265 cm and 210 cm was reached in males and females, respectively. which is the highest for any living species except humans.

Geographic range and distribution

Northern right whale dolphins are found in cold to temperate waters, , of the North Pacific Ocean. They typically inhabit offshore, oceanic regions between 34°N to 55°N and 145°W to 118°E. However, L. borealis has been reported as far south as 29° N, off Baja California (Mexico), during times of anomalously cold water temperatures. Overall, distributions appear to shift northward in summer and southward in winter. However, contradicting patterns have also been observed whale watching companies operating off Monterey.

Behavior

Northern right whale dolphins are fast swimmers. Their average swimming speed is around but they can reach speeds of up to . L. borealis have repetitive burst-pattern pulses that can be categorised and associated to different subgroups of L. borealis. These vocalisations may be used in the communication between individuals, in a similar way to signature whistles in other delphinid species. The epithet of the genus was derived from Greek lisso, smooth, and delphis; the specific epithet, borealis, indicates the northern distribution. Together with the second species of Lissodelphis, Lissodelphis peronii, they are called right whale dolphins because similarly to the right whales (Eubalaena) these dolphins also lack a dorsal fin.

Based on the analysis of complete cytochrome b sequences, LeDuc et al. (1999)

Genetically, no statistically significant differences have been found between northern right whale dolphins from the US coast and other regions within the North Pacific.

Population status

It is estimated that a total of around 68,000 northern right whale dolphins inhabit the Pacific Ocean.

Threats

In the 19th century, whalers occasionally took northern right whale dolphins. In the mid-20th century, the largest threat for L. borealis were drift nets used for large-scale squid fishing. This is thought to have reduced the stock in this area by one- to three-quarters.

It is thought that in contrast to coastal areas, the offshore habitat of the northern right whale dolphin is generally less susceptible to human pollution.

Natural predators of Lissodelphis borealis are unknown, but may include the killer whale (Orcinus orca) and large sharks.

References

More information about the northern right whale dolphins of the east Pacific can be found at the websites of NOAA (National Oceanic and Atmospheric Administration) Furthermore, these YouTube videos show the surface behaviour of a superpod of northern right whale dolphins and the typical sounds that they produce.

References

  • Whale and Dolphin Conservation Society
  • Voices in the Sea – Northern right Whale Dolphin